1. Field of the Invention
This invention relates to electronic data storage systems, particularly to circuits for testing magnetic recording systems.
2. Description of the Background Art
Systems for recording electronic signals in magnetic media perform two basic operations: writing signals to the media, and reading recorded signals from the media. In conventional recording systems, these operations are performed by separate read and write circuits.
If functional problems occur during the operation of the recording system, various tests may be performed to isolate possible problem sources, e.g., either to the magnetic media, the read circuit, or the write circuit. Because such problems often arise in the magnetic media, it is desirable to provide a circuit which initially tests the read and write circuits, thereby quickly eliminating the read and write circuits as potential problem sources.
Accordingly, test circuits, known as "loop-back" circuits, are provided for testing read and write circuits in magnetic recording systems. Generally, loop-back circuits operate by sending signals from the write circuit to the read circuit, while such circuits are disconnected from the magnetic head. In this way, the loop-back circuit may determine whether the read and write circuits are functioning correctly.
Because conventional loop-back circuits disconnect the read and write circuits from the read-write head during testing, functional problems in the head are not detectable by such loop-back circuits. Also, when used for testing recording systems known as disk-duplication systems, wherein multiple signal channels are used for reading or writing simultaneously to both sides of a magnetic disk, loop-back circuits may give rise to signal interference between such channels. This cross-coupling problem might occur, for instance, when loop-back circuits are positioned closely to sensitive read or write circuits.
Loop-back circuits have not been used widely in low-cost recording systems because loop-back circuits are relatively complex and typically require a number of components, such as switch relays and transformers, which increase the cost of each system. For example, to operate properly, each loop-back circuit must include a circuit for modifying the signal sent from the write circuit to the read circuit. The modifying circuit is needed to attenuate the write signal, which is typically several thousand times higher in amplitude than signals provided properly to the read circuit.
Moreover, in digital recording systems, the modifying circuit is needed to process write signals by simulating the signal differentiation which occurs during digital recording read-back. Thus, during write-signal processing, the modifying circuit produces a simulated differentiation of the write signal so that such simulated signal may be received properly by the read circuit.
It would be desirable, therefore, to provide an improved circuit for testing magnetic recording systems, wherein read-write head testing is enabled, and signal interference and component count are reduced.